Spam is a general term for unwanted data or voice messages delivered through a telecommunications network. Spam is a particular problem in short message service and e-mail. For example, spam short messages account for an estimated three quarters of a yearly total of five trillion short message service (SMS) messages worldwide. The prevalence of spam and the relative ease of transmitting spam at low cost have created a near crisis in short message service because spam uses so much of the telecommunications resources of SMS.
Spammers usually send spam messages to mobile end users by mobile telephone numbers either in a fixed range or randomly selected. For example, Spammers in China generate mass spam messages from a personal computer and send these to the public using telephone numbers with the last four digits in the range 0000 to 9999. Some spammers send spam messages to particular groups of end users, for example, when end users subscribe to a new service by intercepting the telephone numbers of the new end user subscribers.
There have been many mechanisms and applications developed for screening and blocking spammer messages, either at the network or at the SMS center (SMSC). However, even with current advanced technologies an estimated 10% of spam messages can go through the anti-spam filtering and reach the end users. Considering the huge number of spam messages being generated today, even receiving a small percentage of spam messages will still cause dissatisfaction to end users and waste large amount of SMS resources.